As most electronic equipment including personal computers, digital cameras and mobile phones become of smaller size and better performance, there is an increasing demand for semiconductor devices of small size, thin profile and high density. There is a desire to have a photosensitive dielectric material which can accommodate an increase of substrate area for productivity improvement and which can accommodate structures having fine asperities with a high aspect ratio on substrates in the high-density packaging technology as typified by chip size packages or chip scale packages (CSP) or 3D layer stacks.
With respect to the photosensitive dielectric material mentioned above, JP-A 2008-184571 discloses a photo-curable resin composition which can be coated to form films having a widely varying thickness by the spin coating technique commonly used in the semiconductor device fabrication, processed into fine size patterns using radiation of a wide wavelength range, and post-cured at low temperatures into electric/electronic part-protecting films having flexibility, heat resistance, electric properties, adhesion, reliability and chemical resistance. Advantageously, the spin coating technique is capable of simply forming a film on a substrate.
This photo-curable resin composition for forming electric/electronic part-protecting films is used to form a film having a thickness of 1 to 100 μm on a substrate. As the film thickness increases beyond 30 μm, it becomes difficult to apply the photo-curable resin composition onto the substrate by spin coating because the composition must have a very high viscosity. The film formation on substrate by spin coating encounters a certain limit in the practical application.
Also, when the photo-curable resin composition is applied onto a substrate having a rugged surface by spin coating, it is difficult to form a uniform layer on the substrate. The photo-curable resin layer tends to leave voids near steps on the substrate. Further improvements in planarity and step coverage are desired. Another coating technique replacing the spin coat technique is spray coating as disclosed in JP-A 2009-200315. Owing to the principle of spraying, defects are often formed including height difference arising from asperities on the substrate, film rupture at pattern edges and pinholes at recess bottom. The problems of planarity and step coverage still remain unsolved.
Recently, in the high-density package technology as typified by chip scale packages (CSP) or 3D stacked packages, a focus is put on the technique of redistribution from chips by forming a fine, high aspect ratio pattern on a substrate and depositing a metal such as copper on the pattern. To meet a demand for chips of higher density and higher integration, it is strongly desired to reduce the width of pattern lines and the size of contact holes for interconnection between substrates in the redistribution technology. The lithography is generally used for forming fine size patterns. In particular, the lithography combined with chemically amplified negative resist compositions is best suited for forming fine pattern features. Since the pattern used for redistribution is permanently left between device chips, the pattern material must have a cure ability and also serve as an electric/electronic part-protecting film having flexibility, heat resistance, electric properties, adhesion, reliability and chemical resistance. For this reason, a negative resist composition is believed suitable for forming such patterns.
Accordingly, a chemically amplified negative resist composition is typical of the pattern-forming material which can be processed into a fine redistribution layer and serve as an electric/electronic part-protecting film having flexibility, heat resistance, electric properties, adhesion, reliability and chemical resistance.
On the other hand, a chemically amplified negative resist composition can form a fine pattern as used in the redistribution technology and is useful as electric/electronic part-protecting film. The negative resist composition is thus often used to cover Cu wirings preformed on substrates, Al electrodes on substrates, or dielectric or SiN substrates having wirings or electrodes formed thereon. Sometimes, the negative resist composition must entirely cover the SiN substrate. Since the adhesion between the coating layer of the negative resist composition and the substrate is still insufficient, a stripping problem often arises that the coating layer is stripped from the substrate.
When the chemically amplified negative resist composition useful to form electric/electronic part-protecting film is patterned, an organic solvent is used as the developer. It is necessary that the exposed region of resist film be turned insoluble in the organic solvent developer via crosslinking reaction or the like while the unexposed region be fully dissolved in the organic solvent developer. Most of commonly used negative resist compositions have a low dissolution contrast, that is, a small difference of solubility in organic solvent developer between the exposed and unexposed regions. A resist composition with a low dissolution contrast is not expectable to form a pattern which is satisfactory with respect to the requirement for finer size patterns. Also when a pattern is exposed and transferred through a mask, a resist composition with a low dissolution contrast may fail to form a pattern faithful to the mask on the substrate. Accordingly, the resist composition is desired to have as high a dissolution contrast as possible, that is, an improvement in resolution is desired.
Furthermore, for the chemically amplified negative resist composition capable of forming a fine size pattern used in processing of interconnects, and useful to form electric/electronic part-protecting film, it is important that the unexposed region is fully dissolved in the organic solvent developer. If the solubility of the unexposed region in the organic solvent developer is low, then it is often observed that film residue or scum is left at the bottom of the pattern, or the pattern is degraded by footing at the root of the pattern on the substrate, particularly when the coating of the resist composition on the substrate is thick. Since such scumming or footing can cause breakage or damage to the electric circuit and interconnect during the redistribution step, it is necessary to inhibit scumming or footing.
Accordingly, to meet a demand for chips of higher density and higher integration, it is desired to have a chemically amplified negative resist composition which can form a fine size pattern for redistribution, and is suited as electric/electronic part-protecting film. The resist composition is further desired to dramatically improve its adhesion to substrate, further improve its resolution performance, and eliminate the problem of footing or scumming at the pattern bottom.